The subject of the present invention is a rewinding machine for winding material in web form onto a core to form rolls, as well as a corresponding winding method.
It is known that the winding of rolls of web material onto cores such as, for example, the winding of paper tissue onto cardboard cores, is performed by means of plant comprising apparatus for continuously unwinding paper from a reel. Downstream of this apparatus there is a winder or rewinding machine which winds the paper onto a plurality of cores to form the rolls. Downstream of the rewinding machine in turn there is apparatus for cutting the finished roll into a plurality of small rolls.
In particular, two methods are known for winding the web material onto the core.
In a first method, known as central winding, the core is fitted on a motor-driven spindle of the same length as the core, for rotating the core about its axis. When an edge of the web material has been stuck to the core, the desired quantity of web material is wound onto the core by rotation of the spindle, to form the roll. Upon completion of the winding, the roll is removed from the working area and the spindle is taken out of the core and returned to the working area by a recirculating device.
A machine of the type described above is known from U.S. Pat. No. 5,660,350.
Although these machines have considerable advantages, they have the disadvantage that it is necessary to use spindles and cores of limited axial length. In fact, during the roll-forming step, long cores fitted on long spindles would clearly be subject to bending forces which would set up vibrations such that accurate and even winding with uniform compactness throughout the winding operation would be impossible, resulting in an irreparable deterioration in the quality of the product.
A second method also used for winding web material onto cores is known as peripheral winding. According to this method, after the core has been brought up to winding drums so as to cause the web material to adhere to the core, the core is driven by the drums in a winding area in which the roll being formed is acted on peripherally by three drums, leaving the core free to float in the web material which is being wound thereon.
A machine of the type described above is known from WO 99/42393 in which, upon completion of the winding, the core is removed from the wound roll, to form rolls without support cores.
However, it is clear that, although this latter solution is simpler in operation, it has many disadvantages.
First of all, peripheral winding, by its nature, does not allow the rate of rotation of the core to be controlled directly since the core is floating in the winding area between the three winding drums. With these known rewinding machines, it is therefore impossible to control the tension of the web material directly during its winding around the core, making it particularly difficult to produce rolls which have a uniform consistency throughout their thickness. This disadvantage is particularly important above all when a particularly soft roll is to be produced, as is required by some markets such as, for example, the United States market. In particular, if the web material is supplied without considerable pretensioning, it is almost impossible to ensure the same compactness of the roll both in the initial stages of the winding and in the final stages of the winding and, in the case of particularly soft rolls, the core may even be eccentric relative to the axis of the roll upon completion of the winding.